杏吧原创

TERMITES have devised an ingenious public health programme. By vaccinating their nest mates against infection, they prevent potentially devastating diseases destroying the colony, entomologists have discovered. This group immunity could be one reason why social insects are so successful.

Many social insects such as bees, wasps and ants cooperate to keep parasites at bay. Ants, for example, shift dead workers out of their colonies to prevent disease spreading (New 杏吧原创, 24 November 2001, p 19), and bees get together to warm up parts of the hive infected with a fungal epidemic. This 鈥渃olony fever鈥� helps kill off the parasite.

Now James Traniello and his team at Boston University in Massachusetts have found that living in a group boosts an individual termite鈥檚 immunity to disease. He had shown previously that termites that survive an infection are better able to fight off the same disease in future, suggesting that their immune system develops a 鈥渕emory鈥� for the parasite, just as ours does. Traniello now wanted to find out whether this memory could be transferred between nest mates.

The researchers exposed dampwood termites (Zootermopsis angusticollis) to a fungal infection to immunise them. Next, they placed the immunised insects with termites that had never encountered the fungus. When they infected different groups of termites with the fungus, they found that unimmunised termites did better in these mixed groups than in a group on their own. The immunised insects are carrying out a sort of 鈥渟ocial vaccination鈥�, says Traniello.

As yet, the team doesn鈥檛 know how immunity is transferred. But Traniello has a few ideas. Termites regularly transfer gut bacteria to each other, which allows them to break down cellulose in wood. So they may be sharing fungicides produced by bacteria in their guts in the same way. Alternatively, the immunised termites might transfer inactivated fungal spores to their nest mates, which allows them to experience the pathogen safely.

鈥淭his is a very original idea,鈥� says Bert H枚lldobler, an expert in social insects at the University of W眉rzburg in Germany. He speculates that immunity transfer could be an important benefit of social living.

But Francis Ratnieks of the University of Sheffield cautions against claiming social vaccination as the factor that drove termites to live socially in the first place. We know very little about termites鈥� ancestors, he says, and they probably evolved the vaccination strategy after the switch to social living.